This application is based on and claims under 35 U. S. C. xc2xa7119 with respect to Japanese Application No. 2000-179055 filed on Jun. 14, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to variable valve timing systems. More particularly, the present invention pertains to a variable valve timing system for controlling the opening and closing time of an intake valve and an exhaust valve of a vehicle engine.
A known variable valve timing system is described in Japanese Patent Laid-Open Publication H09-324613. The disclosed variable valve timing system includes a housing member disposed in the driving force transmitting system for transmitting the driving force from the crankshaft of the combustion engine to the camshaft to control the opening and closing of either one of the intake valve and the exhaust valve of the combustion engine. The housing member rotates as a unit with either one of the crankshaft or the camshaft.
The variable valve timing system also includes a rotor member rotatably assembled on a shoe portion provided on the housing member. The rotor member forms an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member and integrally rotates with either one of the camshaft or the crankshaft. The variable valve timing system further includes a relative rotation controlling mechanism. The relative rotation controlling mechanism allows relative rotation of the housing member and the rotor member through an unlock operation by the supply of an operation fluid. The relative rotation controlling mechanism restricts the relative rotation of the housing member and the rotor member at an intermediate angle phase between the most retarded angle phase and the most advanced angle phase through the lock operation by the discharge of the operation fluid.
The variable valve timing system still further includes a hydraulic pressure circuit for controlling the supply and discharge of the operation fluid to the relative rotation controlling mechanism as well as for controlling the supply and discharge of the operation fluid to the advanced angle chamber and the retarded angle chamber.
In this known variable valve timing system, the relative rotation controlling mechanism restricts the relative rotation of the housing member and the rotor member at the intermediate angle phase between the most retarded angle phase and the most advanced angle phase. Under this condition, the opening and closing time of either one of the intake valve and the exhaust valve is set in order to obtain a good starting performance of the combustion engine. Accordingly, when the combustion engine is started, if the relative rotation of the housing member and the rotor member is not restricted by the relative rotation controlling mechanism at the intermediate angle phase between the most retarded angle phase and the most advanced angle phase, the starting performance of the combustion engine might be adversely affected.
The restriction of the relative rotation of the housing member and the rotor member by the relative rotation controlling mechanism at the intermediate angle phase when the combustion engine is started may be interrupted by the design of the hydraulic pressure circuit, and by a remaining operation fluid in the advanced angle chamber, the retarded angle chamber, and the relative rotation controlling mechanism. In the known hydraulic pressure circuit, when a controlling valve provided in the hydraulic pressure circuit is de-energized, the operation fluid is set to be supplied to the advanced angle chamber or the retarded angle chamber. In the known hydraulic pressure circuit, when the combustion engine is started, if the controlling valve is de-energized, the operation fluid is supplied to the advanced angle chamber or the retarded angle chamber. Then the rotor member might not rotate relative to the housing member at the intermediate angle phase.
A need thus exists for a variable valve timing system in which a hydraulic pressure circuit controls the supply and discharge of an operation fluid to a relative rotation controlling mechanism and controls the supply and discharge of the operation fluid to an advanced angle chamber and a retarded angle chamber.
The present invention provides a variable valve timing system including a hydraulic pressure circuit for controlling the supply and system discharge of an operation fluid to a relative rotation controlling mechanism while also controlling the supply and discharge of the operation fluid to an advanced angle chamber and a retarded angle chamber. The hydraulic pressure circuit is adapted to discharge the operation fluid from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism when the combustion engine is started.
The present invention also provides a variable valve timing system including the hydraulic pressure circuit for controlling the supply and discharge of the operation fluid to the relative rotation controlling mechanism while also controlling the supply and discharge of the operation fluid to the advanced angle chamber and the retarded angle chamber. The hydraulic pressure circuit is adapted to discharge the operation fluid from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism when the supply and discharge control of the operation fluid is defective.
When used in a variable valve timing system for an automobile, the operation fluid is desirably discharged from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism by a single controlling valve provided in the hydraulic pressure circuit. Alternatively the operation fluid is desirably discharged from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism by a plurality of controlling valves provided in the hydraulic pressure circuit.
According to the present invention as noted above, the hydraulic pressure circuit is adapted to discharge the operation fluid from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism when the combustion engine is started. Accordingly, when the combustion engine is started, operation fluid remaining in each of the advanced angle chamber and the retarded angle chamber can be discharged. The relative rotation of the housing member and the rotor member is thus not interrupted by the operation fluid, and the rotor member can rotate quickly relative to the housing member to the intermediate phase position between the most advanced angle phase position and the most retarded angle phase position by the torque variation from the driving force transmitting system. When the combustion engine is started, the operation fluid can be discharged from the relative rotation controlling mechanism and so the appropriate lock operation can be obtained by the relative rotation controlling mechanism. The relative rotation of the housing member and the rotor member is appropriately restricted at the intermediate phase position. Accordingly, the starting performance of the combustion engine can be improved.
Also in accordance with the present invention as noted above, the hydraulic pressure circuit is adapted to discharge the operation fluid from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism when the combustion engine is actuated and when the supply and discharge control of the operation fluid is defective. Accordingly, when the supply and discharge controlling of the operation fluid is defective, the operation fluid remaining in each of the advanced angle chamber and the retarded angle chamber can be discharged. The relative rotation of the housing member and the rotor member is thus not interrupted by the operation fluid, and the rotor member can rotate quickly relative to the housing member to the intermediate phase position between the most advanced angle phase position and the most retarded angle phase position by the torque variation from the driving force transmitting system. When the supply and discharge control of the operation fluid is defective, the operation fluid can be discharged from the relative rotation controlling mechanism and so the appropriate lock operation can be obtained by the relative rotation controlling mechanism. Also, the relative rotation of the housing member and the rotor member is appropriately restricted at the intermediate phase position and so the starting performance of the combustion engine can be improved when the supply and discharge controlling of the operation fluid is defective. Further, the combustion engine is actuated under the condition of the combustion engine fulfilling the minimal functions.
According to the variable valve timing system in which the operation fluid is adapted to be discharged from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism by a single controlling valve provided in the hydraulic pressure circuit, the hydraulic pressure circuit can be simply and compactly configured.
Alternatively, when the operation fluid is adapted to be discharged from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism by a plurality of controlling valves provided in the hydraulic pressure circuit, a conventional or known controlling valve (the controlling valve in which the operation fluid is set to be supplied to the advanced angle chamber or the retarded angle chamber when the controlling valve is de-energized) can be used as one of the plurality of controlling valves.
According to another aspect of the present invention, the variable valve timing system includes a housing member provided in a driving force transmitting system for transmitting a driving force from a crankshaft of a combustion engine to a camshaft for controlling the opening and closing of either one of an intake valve or an exhaust valve of the combustion engine, with housing member rotating as a unit with either one of the crankshaft or the camshaft, a rotor member rotatably assembled relative to the housing member and forming an advanced angle chamber and a retarded angle chamber in the housing member, with the rotor member rotating as a unit with either one of the camshaft or the crankshaft, and a relative rotation controlling mechanism allowing relative rotation of the housing member and the rotor member by an unlock operation through supply of an operation fluid, and restricting the relative rotation of the housing member and the rotor member at an intermediate angle phase between a most retarded angle phase and a most advanced angle phase by a lock operation through discharge of the operation fluid. A hydraulic pressure circuit controls the supply and discharge of the operation fluid to the relative rotation controlling mechanism and controls the supply and discharge of the operation fluid to the advanced angle chamber and the retarded angle chamber. The hydraulic pressure circuit includes an operation fluid source that supplies the operation fluid, a reservoir and a hydraulic pressure controlling valve having a first connecting port connected to the advanced angle chamber, and a second connecting port connected to the retarded angle chamber. The hydraulic pressure controlling valve communicates the first connecting port and the second connecting port to the reservoir when the combustion engine is started and/or when supply and discharge control of the operation fluid is defective.